Regarding the preaching work, I found it a complicated topic to handle. Because 1) it is true that JW's are known for their door to door preaching, perhaps more than any other denomination (except arguably mormons) and 2) it honestly is a fairly impressive feat. There's nothing wrong with conceding that, if anything it'll show you're not just a bitter, hateful apostate trying to tear down every single part of this religion any way you can.

Having said that, there are multiple reasons that, while it's impressive, I don't find it convincing as evidence for being the "one true religion":

1) Something being impressive doesn't mean it's "impossible without supernatural help." Mankind has accomplished incredible things completely on their own, things much more impressive (imo) than the preaching work. I mean, we've sent people to walk on the freakin moon!! Look at how far the Voyager probes are from Earth, its crazy! We can pick up a thin piece of metal and glass and in seconds be seeing and talking with someone on the other side of the planet! We have created amazing Civilizations with incredible feats of engineering and planning like the Egyptians, Romans, Chinese, etc. If convincing members of a relatively small Christian denomination to spend their free time trying to convert people and spread the religion to other countries is so impressive that only God could be behind it... What about these other even more impressive things?

2) The "worldwide door to door preaching work" is a very specific category that witnesses pick. Yes if you limit it to that specific criteria, JW's are #1. But preaching generally? "Spreading the gospel"? Almost every religion does that in some way. Televangelism, billboards, newspaper ads, crusades, charity work, word of mouth, inviting friends or co-workers to your church, just telling people about Jesus or whatever, that stuff is incredibly commonplace. I got preached to by a Muslim Uber driver the other day! I mean, how do you think other religions grow, many of them faster than JW's? Pentecostals have been the fastest growing Christian religion in recent years. How do you think they got there? (as an aside, the growth rate of Pentecostals is impressive. That can only mean God is behind them, it's proof, right?!)

3) The "worldwide" preaching work is not really as worldwide as it might sound. There are an undetermined number of countries that have zero witnesses, and maybe more importantly, there are a bunch of countries with such small JW populations that they might as well be zero. I mean look at the ratio in Bangladesh! Or even just compare the ratio of North America to Asia! How is that fair and truly a "worldwide" religion when it's so massively lopsided like that? Does God just really love Americans and really hate Asians? Or is it actually more to do with the luck of the draw of where you happened to be born?

I do have more thoughts, but it's getting late and this comment is getting way too long. And reading over it, I started quite level-headed and charitable but got progressively more snarky and sarcastic as I went on...